This application is based on and incorporates herein by reference Japanese patent application No. 2000-74462 filed Mar. 16, 2000.
The present invention relates to a motor and a motor for a wiper device having a noise suppressing choke coil and a burn-out protector.
A motor for a wiper and the like having a noise suppressing choke coil and a circuit breaker (breaker) serving as a burn-out protector is known. The choke coil and the breaker are connected in series with each other between a power supply brush which slides in contact with a commutator and an external power supply. The breaker is disposed in the vicinity of the commutator and a winding together with the brush.
In the motor of this type having the noise suppressing device, upon application of a direct current (DC) voltage thereto from the external power supply, the armature generates a magnetic field and the armature (rotor) rotates. At this time, electrical noise is generated due to a sliding contact between the brush and the commutator. The electrical noise is attenuated by the inductance of the choke coil. Accordingly, the electrical noise is propagated decreasingly to the external DC power supply, and radiation of an electromagnetic noise due to the electrical noise is restricted.
In the motor, when the winding of the armature generates heat owing to an excessively high current caused by a high load applied to the output side during the rotation of the rotor, the breaker is placed in an unconnected state owing to the heat generated by the winding of the armature and the heat generated by the breaker itself. Consequently, the breaker responds to this heat and cuts off electric current supply to the motor. Therefore, it is possible to prevent burn-out based on the heat thus generated.
However, a large number of members such as a spring for urging the brush toward the commutator and electric wires are disposed in the vicinity of the brush. Thus, it is difficult to dispose the breaker in the vicinity of the brush, commutator and the winding, particularly when the motor is sized small.
It is proposed to solve this drawback that the breaker is disposed apart from the armature and operated by only heat generated thereby. However, it is necessary to increase the internal resistance value of the breaker to operate it by only the heat generated thereby. Consequently, an internal resistance-caused voltage drop increases, and the efficiency of the motor decreases.
It is an object of the present invention to provide a motor and a motor for a wiper device which allows a burn-out protector to be easily disposed without decreasing the efficiency of the motor.
According to the present invention, a motor comprises brushes for a commutator, noise suppressing coil devices connected in series with the brushes, and a burn-out protector which prevents a motor burn-out caused by excessively high current. The burn-out protector is disposed in the vicinity of the coil devices to cut off electric current supplied to the brushes in response to heat generated by the coil devices.
Preferably, the burn-out protector is surrounded by the coil devices, and connected in series with a common brush which is used in common for a high-speed driving brush and a low-speed driving brush which are selectively used.